Nano-structural effects on gene transfection: large, botryoid-shaped

nanoparticles enhance DNA delivery via macropinocytosis and

effective dissociation

Wenyuan Zhang a,b, Xuejia Kang a,c, Bo Yuan d, Huiyuan Wang a, Tao Zhang a, Mingjie Shi a,

Zening Zheng a,c, Yuanheng Zhang a, Chengyuan Peng a, Xiaoming Fana, Youqing Shen e,

Yongzhuo Huang a,b *

a State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese

Academy of Sciences, Shanghai 201203, Chinab University of Chinese Academy of Science, Beijing, 100049, Chinac Institute of Tropical Medicine, Guangzhou University of Chinese Medicine, Guangzhou

510405, Chinad Affiliated Hospital of Shandong University of Traditional Chinese Medicine, Jinan 250011,

Chinae College of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027,

China

Corresponding authors:

* Yongzhuo Huang, Ph.D.

Professor of Pharmaceutics

Shanghai Institute of Materia Medica, Chinese Academy of Sciences

501 Haike Rd, Shanghai 201203, China

Tel/Fax: +86-21-2023-1981

Email: yzhuang@simm.ac.cn

1

Graphic abstract

2

Abstract

Effective delivery is the primary barrier against the clinical translation of gene therapy. Yet

there still remains too much unknown in the gene delivery mechanisms, even for the most

investigated polymeric carrier (i.e., PEI). As a consequence, the conflicting results have been

often seen in the literature due to the large variability in the experimental conditions and

operation. Therefore, some key parameters should be identified and thus strictly controlled in

the formulation process.

Methods: The effect of the formulation processing parameters (e.g., concentration or mixture

volume) and the resulting nano-structure properties on gene transfection have been rarely

investigated. Two types of the PEI/DNA nanoparticles (NPs) were prepared in the same

manner with the same dose but at different concentrations. The microstructure of the NPs and

the transfection mechanisms were investigated through various microscopic methods. The

therapeutic efficacy of the NPs was demonstrated in the cervical subcutaneous xenograft and

peritoneal metastasis mouse models.

Results: The high-concentration process (i.e., small reaction-volume) for mixture resulted in

the large-sized PEI/DNA NPs that had a higher efficiency of gene transfection, compared to

the small counterpart that was prepared at a low concentration. The microstructural

experiments showed that the prepared small NPs were firmly condensed, whereas the large

NPs were bulky and botryoid-shaped. The large NPs entered the tumor cells via the

macropinocytosis pathway, and then efficiently dissociated in the cytoplasm and released

DNA, thus promoting the intranuclear delivery. The enhanced in vivo therapeutic efficacy of

the large NPs was demonstrated, indicating the promise for local-regional administration.

Conclusion: This work provides better understanding in the effect of formulation process on

nano-structural properties and gene transfection, laying a theoretic basis for rational design of

the experimental process.

Keywords: gene delivery; PEI; macropinocytosis; TRAIL; clathrin; local-regional gene

therapy

3

1. Introduction

The common purpose of gene delivery is to deliver the therapeutic nucleic acids from the

application site to the pathological tissues, following by intracellular transport, and targeting

the specific cytoplasm components or the nucleus [1]. PEI has become one of the most

commonly used non-viral gene vectors due to its high transfection efficiency in mammalian

cells and ready availability. Despite the extensive application of the PEI, the conflicting

results of PEI-mediated transfection have been often seen in literature. It could be accounted

for the large variability in the experimental conditions and operations in transfection

experiments [2-4]. It is known that the transfection efficiency of the PEI/DNA NPs is

affected by the N/P ratio of PEI and DNA, serum content of culture medium, and etc. Indeed,

such changes resulted in the difference of particle size and surface charge, and consequently

the transfection efficacy.

The formation of the PEI/DNA nanocomplex is first driven by the electrostatic interaction

and finally by entropy, when mixing the positive charges of the PEI and the negative charges

of the DNA together [5, 6]. Therefore, such formation is highly dynamic and variable,

heavily affected by the parameters of the process. There still remains much room to explore

because the mechanisms of PEI-mediated transfection have not been well understood yet [1,

2, 7]. Usually, much attention has been placed in how the changing ratio of the two reagents

of the PEI/DNA affected the transfection efficiency. For example, a low N/P ratio of

PEI/DNA tends to form the large-sized complexes, while a high N/P ratio was the opposite

[8]. Moreover, the use of different molecular weight of PEI was also a major factor for

controlling particle size; for example, low-molecular-weight PEI generally exhibited weaker

condensation ability to DNA than the high-molecular-weight PEI, thus resulting larger

particle size [8].

However, the operational changes of the process may affect the physicochemical

properties and the transfection results as well. Unfortunately, it is little known about the

influence of the operational changes on the resulting PEI/DNA NPs. For example, it is often

seen in literature the variable transfection results even with the same dose of PEI/DNA and

the cell lines. Usually, the PEI/DNA ratio or dose is reported as a key parameter in literature,

but the operation concentration and liquid volume are largely ignored and missed in the

reports. From an aspect of pharmaceutical engineering, the setting of the processing

parameters is also an essential consideration for formulation. Yet, the important effect of the

process setting on transfection has not been realized.

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In this study, we demonstrated the significant effect of the operation concentration or

mixture volume on the formation of the nanocomplex of PEI/DNA, as well as their size and

morphology. Moreover, it was also demonstrated that the large-sized NPs possessed

enhanced gene transfection efficiency and the promising application in local-regional

therapies.

2 Results

2.1 The mixture volume affected transfection efficiency of PEI/DNA

At a fixed dose, a small-volume mixture process was related to use a high concentration of

PEI and DNA, and a large-volume process was related to low concentration (Scheme 1). It

was revealed that the mixture volume of PEI and DNA is a key factor of the formulation

process for controlling the transfection of the PEI/DNA NPs. A small-volume process (i.e.,

high concentration of PEI and DNA, termed PEI/DNAhigh) resulted in better efficacy. The

cellular uptake study of the NPs was conducted in the HeLa cells using flow cytometry and

confocal microscopy. For both the NPs at the same dose, the fluorescent positive rate was

greater than 80% (i.e., PEI/DNAlow 82% and PEI/DNAhigh 91%) (Figure 1A–C). However,

the total fluorescence intensity of the PEI/DNAhigh group showed a 3.7-fold increase,

compared to the PEI/DNAlow (Figure 1D). The fluorescence intensity results suggested that

there was a greater amount of the PEI/DNAhigh NPs in cellular uptake.

The gene transfection efficiency of these two NPs was investigated. In Figure 2A–D,

peGFP-N1 was used as the reporter gene; consistent with the cellular uptake results, the

transfection positive rate of the PEI/DNAhigh NPs was significantly higher, displaying 4.9-fold

higher than that of the PEI/DNAlow NPs (Figure 2C). Accordingly, the total fluorescence

intensity of the PEI/DNAhigh NPs, reflecting the level of GFP expression, was 11.9-fold

higher than that of the PEI/DNAlow NPs (Figure 2D).

Other reporter genes (e.g., the red fluorescence protein-encoding pRFP and luciferase-

encoding pGL4.13) were also applied for the transfection studies, and similar results were

found (Figure 2E-H), both displaying an appropriate 10-fold increase in the PEI/DNAhigh

group.

We further tested the intracellular uptake and transfection efficiency of these two groups

of PEI/DNA NPs in other types of cells. Dendritic cells (DCs) are the most potent antigen-

presenting cells, and the major target for cancer DNA vaccines. The results in DC2.4 cells

and bone marrow-derived dendritic cells (BMDCs) also showed that the PEI/DNAhigh NPs

had the enhanced cellular uptake and gene transfection compared to the PEI/DNA low NPs

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(Figure S1). Moreover, it was also found that the PEI/DNAhigh NPs had the enhanced gene

transfection compared to the PEI/DNAlow NPs in the MCF-7 cells, H/T cells and A549T cells

(Figure S2).

The branched PEI25k was also used to investigate. Similarly, the b-PEI/DNAhigh NPs had

larger particle size compared to the b-PEI/DNAlow NPs (542 nm vs 75 nm) (Figure S3A). It

was also observed that the b-PEI/DNAhigh NPs improved the gene transfection compared to

the b-PEI/DNAlow NPs (Figure S3B-D). Moreover, the b-PEI/DNAhigh NPs had the enhanced

gene transfection compared to the b-PEI/DNAlow NPs in MCF-7, H/T and A549T cells

(Figure S4).

2.2 The mixture volume affected the morphology of the PEI/DNA NPs

The findings above were interesting, which inspired us to further investigated the

mechanisms of how the different volume process affected the transfection. The morphology

of these two NPs was examined. It was revealed that a small-volume process (i.e., with high

mixture concentration) resulted in the large particles (denoted as PEI/DNAhigh NPs),

compared the large-volume process that led to the small particles (i.e., denoted as

PEI/DNAlow NPs), displaying 581 nm vs 89 nm. Both of the PEI/DNAhigh and PEI/DNAlow

NPs remained stable in water, HEPES buffer, or the culture medium with FBS (Figure S5A-

C). There was no difference between the two NPs in the zeta potential (Figure S5D-F).

The microstructure of the NPs was investigated by atomic force microscopy (AFM). The

2D and 3D AFM images showed that PEI efficiently condensed DNA and form the particle-

shaped nanocomplex for both PEI/DNAhigh and PEI/DNAlow (Figure 3A). The section

analysis (vertical distance for 2D AFM images) and the particle peak height for 3D images

were analyzed by NanoScope Analysis software. Both of the section analysis and the average

value of particle peak height confirmed the larger size of the PEI/DNAhigh NPs compared to

the PEI/DNAlow NPs (Figure 3B–C).

The internal microstructure of the NPs was observed using the stimulated emission

depletion (STED) microscopy technique by dual-labeling (DNA, green; PEI, red). In the

PEI/DNAlow NPs, DNA was almost co-localized with PEI, demonstrating the compact

condensation, while the PEI/DNAhigh NPs displayed a less compact pattern and a botryoid

shape (Figure 4). It suggested that the formulation process via a small-volume mixture that

was at a high concentration condition resulted in the weak interaction between DNA and PEI,

and the loose structure and large size.

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Ionic polymers contain various amount of charges (e.g., –NH3+ in PEI, and –PO4

-–in

DNA), depending on the ionizing degree in aqueous solution. Our results demonstrated that

PEI at low concentration possessed high zeta potential and large hydrodynamic size (Figure

S6), compared to that at high concentration, indicating the enhanced ionization and extension

of PEI polymer chains at low concentration. As a consequence, the polymers (PEI and DNA)

at low concentration yielded a stronger interaction due to the adequate exposure the charged

segments at each chain. Our conclusion was in accordance with a previous report that the

high degree of ionization for the cationic polymer (poly[2-(dimethylamino)ethyl

methacrylate] or DMAEMA) at a favorable pH resulted in greater binding affinities with

DNA and the compact complexation structure [9].

2.3 The structural difference affected the cellular uptake pathway

The cellular uptake pathway was investigated using the total internal reflection

fluorescence microscopy (TIRFM) for detecting the single cell tracking at a 100-nm

thickness. As shown in Figure 5, Supplementary Video 1, and Figure S7, there was an

interesting phenomenon that the PEI/DNAhigh NPs interacted with the pseudopod-like

extension of the cell and was then engulfed by the cells. The cellular uptake of the

PEI/DNAhigh NPs was analyzed by single-particle tracking (SPT) technique. SPT was a

technique using the tracking algorithm to address the principal challenges such as particle

motion heterogeneity, high particle density, temporary particle disappearance, and particle

splitting. The algorithm first links the particles between consecutive frames, and then links

the resulting track segments into complete trajectories [10].

In Figure 5A, the cellular uptake of the PEI/DNAhigh NPs (red) was clearly tracked the

process from outside of the cells to entering the cells; and the trajectory of the bulky NPs was

shown in amplification (Figure 5B). In Figure 5C (Supplementary Video 2), the cellular

uptake of the PEI/DNAhigh NPs was real-time tabbed with the trajectories. The normalized

lifetime histogram of trajectories was shown in Figure 5D. The mean square displacement of

the PEI/DNAhigh NPs, representing the diffusion coefficient of particles, was analyzed during

its movement outside and inside the cell (Figure 5E). It indicated two different movements

of the bulky NPs when it was in or out of the cell. The trajectory of the PEI/DNA high NPs in

Figure 5C was shown as x coordinate, y coordinate and amplitude over time (Figure 5F).

And no particle splitting events were found, suggesting there was no disassociation during the

cellular uptake. These results indicated that the pseudopod-mediated mechanism could be

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involved in the cellular uptake of the large PEI/DNAhigh NPs. It has been reported that the

pseudopod interaction was a pathway for the cellular uptake of a bacteria [11].

2.4 Endocytosis pathway study

To investigate the endocytosis pathway, the cells were pre-treated with various endocytosis

inhibitors (chlorpromazine, an inhibitor of clathrin-mediated endocytosis [12]; nystatin, an

inhibitor of caveolae-mediated endocytosis [13]; or cytochalasin D, an inhibitor of

macropinocytosis) [14], and then conducted the gene transfection experiments. peGFP-N1

was used as the reporter gene. The relative positive rate of transfection and protein expression

level in the cells were quantitatively analyzed by FACS.

Chlorpromazine treatment dramatically decreased the relative positive rate of transfection

and protein expression level in the PEI/DNAlow NPs group, but no major impact on the

PEI/DNAhigh NPs group (Figure 6A, B). It indicated that clathrin-mediated endocytosis was a

primary mechanism for the PEI/DNAlow NPs. By contrast, cytochalasin D treatment led to the

remarkable decrease in the relative positive rate of transfection and protein expression level

in the PEI/DNAhigh NPs group but yielded minor effect on the PEI/DNAlow NPs group (Figure

6C, D). It revealed macropinocytosis was a main pathway for the PEI/DNAhigh NPs. Nystatin

(< 20 µM) yielded very minor inhibition of transfection in both the NPs, suggesting that

caveolae-mediated endocytosis was not essential for both NPs (Figure 6E, F).

The clathrin-mediated endocytosis pathway for NPs was size-dependent, showing an

observed upper limit for internalization of about 200 nm [15]; therefore, the NPs with a size

under 200 nm was favorable for the clathrin pathway. However, the clathrin-coated vesicles

finally enter the endo/lysosomes, susceptible for degradation, which was disadvantageous to

gene transfection [16, 17]. The macropinosomes may not mature to late endosomes or fuse

with lysosomes [18]. Due to the physical characteristics of leakage of macropinosomes, the

NPs can easily escape into the cytoplasm, which is helpful for facilitating gene transfection

[19, 20]. Moreover, the macropinocytosis can take up the large cargo, which contains the

high amount of DNA, and therefore, it is thought that the macropinocytic pathway provides a

benefit of increasing uptake [21]. The analysis above provided a possible explanation that the

large NPs of PEI/DNAhigh performed higher uptake amount of DNA and more efficient

transfection than the PEI/DNAlow NPs.

2.5 Subcellular distribution of the two groups of PEI/DNA NPs

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The subcellular distribution of the two groups of PEI/DNA NPs was examined. The

lysosome trap is a major barrier against effective gene delivery [22]. DNA is not only

difficult to escape from lysosomes, but also readily enzymatically degraded in lysosomes.

After a 4-h incubation with the NPs that were labeled with YOYO-1 (green), the cells were

observed by confocal laser scanning microscopy (CLSM) followed by LysoTracker Red

DND-99 (red) staining. The co-localization of lysosomes and NPs was showed in 2D and 3D

confocal images (Figure 7A), and the co-localization percentage was 55.6% for the

PEI/DNAlow NPs and 40.5% for the PEI/DNAhigh NPs, quantitatively analyzed by ImageJ

(Figure 7B).

Furthermore, the co-localization of the macropinosomes and the NPs was examined by

using the macropinosome probe dextran rhodamine B and 2D and 3D confocal imaging

(Figure 8A). The significant co-localization indicated by yellow color was observed in the

PEI/DNAhigh NP group. The co-localization percentage was 66.4% for the PEI/DNAhigh NP

group, compared to 38.3% for PEI/DNAlow NP group (Figure 8B). The results further

demonstrated that the macropinocysis was the major mechanism for the enhanced

transfection efficiency of the large PEI/DNAhigh NPs.

2.6 Observation of the disassociation of DNA and PEI in cells

As the PEI/DNAhigh NPs displayed a less compact pattern and a botryoid shape, it was thus

hypothesized that such structure could facilitate the disassociation of DNA from the complex

inside the cells and the subsequent gene transfection.

The disassociation process was observed by fluorescence resonance energy transfer

(FRET) technique. DNA and PEI were labeled with Cy3 (green) and Cy5 (red) dye,

respectively, which were a pair of donor and acceptor used for FRET. The PEICy5/DNACy3

NPs with different mass ratios were measured using a fluorospectrometer. The results showed

that the complexation of PEICy5/DNACy3 resulted in the significantly decreased emission

fluorescence intensity of Cy3 and the increased fluorescence intensity of Cy5 (Figure 9A).

Then the disassociation of the two groups of NPs in the cell was observed by CLSM at 4,

8, and 12 h. Over the time, along with the gradual dissociation of DNACy3 (green) from PEICy5

(red), and the FRET effect weakened. The 3D confocal images (Figure 9B) showed the

fluorescence recovery of DNACy3, which was more obvious in the PEI/DNAhigh NP group than

in the PEI/DNAlow NPs group, suggesting the higher intracellular disassociation efficiency for

the PEI/DNAhigh NPs.

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As shown in Figure 9C, the FRET of the two NPs was gradually decreased from 4 to 12

h, indicating that DNA gradually dissociated from PEI in the cells. The FRET (quenched)

efficiency of the PEI/DNAhigh NPs was lower than the PEI/DNAlow NPs over the time. For

instance, at the 12-h mark, the quenched rate was 68% for the PEI/DNAhigh NPs compared to

78% for the PEI/DNAlow NPs, demonstrating the higher cytoplasmic disassociation of the

PEI/DNAhigh NPs.

2.7 Nuclear uptake of the PEI/DNA NPs

DNA must be delivered into the nucleus to access to the transcriptional machinery. The

nuclear uptake is a key step for transfection. The nuclear uptake percentage of the

PEI/DNAhigh NPs was higher than that of the PEI/DNAlow NPs, analyzed by FACS (Figure

10A). Importantly, the DNA nucleic uptake amount, represented by the total fluorescence

intensity, was also significantly higher in the PEI/DNAhigh NPs group (Figure 10B).

Therefore, the increased intranucleic delivery of DNA was a mechanism underlying its

enhanced transfection efficiency of the PEI/DNAhigh NPs group.

2.8 The in vitro antitumor activity of the PEI/DNA NPs

The pTRAIL DNA was used as a therapeutic gene in this study. After transfection, the

Western blot analysis showed that the expression of TRAIL protein was higher in the large

PEI/pTRAILhigh NPs group (Figure 11A). Accordingly, the PEI/pTRAILhigh NPs also showed

higher antitumor efficacy in the HeLa cells, compared to the PEI/pTRAIL low NPs (Figure

11B).

In addition, the materials-associated cytotoxicity of the PEI/DNA NPs was investigated by

using a blank plasmid DNA. Both groups of NPs did not show obvious cytotoxicity (cell

viability > 90%) at a concentration up to 3 µg/mL, and there was no significant difference

between the two groups (Figure 11B).

2.9 The in vivo therapeutic effects of the PEI/DNA NPs in a cervical tumor xenograft

model

The therapeutic efficacy of the two groups of NPs was investigated in a HeLa cervical

tumor xenograft mouse model. Our previous demonstrated that pTRAIL was a potent

therapeutic gene in various cancers [23-25]. Tumor necrosis factor-related apoptosis-inducing

ligand (TRAIL) is the key protein inducing apoptosis through action on the death receptors

DR4 and DR5 [26].

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Both kinds of NPs inhibited the tumor growth and prolonged survival time. The

PEI/DNAhigh NPs showed a higher inhibition rate of tumor growth of 74.4%, in sharp contrast

to 44.8% for the PEI/DNAlow NPs (Figure 12A–D). The animals receiving PEI/DNAhigh NPs

all survived during the treatment.

Accordingly, the TRAIL expression in the tumors dissected from the mice treated with the

PEI/DNAhigh NPs was higher than that observed in the PEI/DNAlow NP group, as determined

by both Western blotting and immunohistochemistry (Figure 12F–G). Furthermore, the

TUNEL assay in the tumors also exhibited significant apoptosis induced by the PEI/DNAhigh

NPs (Figure 12H). These results were in good agreement with the results of the tumor

inhibition rate.

Interestingly, DR5 upregulation was found in the PEI/DNAhigh NPs (Figure 12F). It was

reported that virus transfection can stimulate the upregulation of DR5 expression [27]. It was

thus suspected that the PEI-mediated transfection could have the similar effect on DR5

upregulation. In addition, the generation of reactive oxygen species (ROS) in the apoptosis

process could contribute to the up-regulation of DR5 [28]. We also found the PEI/DNAhigh

NPs induced the higher intracellular ROS level than the counterpart (Figure S8).

The side toxicity of the NPs was preliminarily evaluated. During the treatment course,

there were no obvious changes in body weight in both NPs groups (Figure S9A). The organ

coefficient (i.e., the ratio of an organ weight to the body weight) of the mice at the

experimental endpoint was not significantly different compared to the control group, except

for a slight increase in the liver coefficient in both groups (Figure S9B). Histological

examination showed no significant pathological changes (Figure S9C). Although PEI is

known for its cytotoxicity, our method that involved a low dose for local application was not

found with unwanted toxicities, rendering it potential for translation. Overall, the results

indicated that the PEI/DNAhigh NPs had better in vivo therapeutic effects than the PEI/DNAlow

NPs due to the enhanced gene transfection efficiency.

2.10 The in vivo therapeutic effects of the PEI/DNA NPs in a peritoneal HeLa tumor

model

The clinical use of local-regional administration in cancer treatment has also been

gradually increased [29]. PEI-based nanomedicines have been used as local-regional gene

therapy for patients with bladder, ovarian and pancreatic cancer in clinical trials [30]. The

therapeutic potential of the large PEI/pTRAIL NPs was further demonstrated by using a

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peritoneal HeLa tumor model, a mimic of late stage of cervical metastasis of peritoneum [31].

Intraperitoneal therapy has been used in peritoneal metastasis for the optimized local drug

delivery and improved clinical outcome [32]. Our results revealed that intraperitoneal

administration of both the PEI/pTRAIL NPs inhibited the tumor growth. The PEI/pTRAILhigh

NPs showed a high inhibition rate of tumor growth of 64.2%, in contrast to 39.1% for the

PEI/pTRAILlow NPs (Figure 13A-D), without obvious side toxicity signs (Figure 13E-F).

3 Discussion

At the cellular level, non-viral vectors consistently are hindered by numerous extra- and

intracellular obstacles, such as cellular uptake, endosomal escape, nuclear entry, transcription

and protein expression [22, 33]. This presented work revealed that the formulation process

parameters (e.g., the mixture volume or concentration) yielded significant impact on gene

transfection of PEI/DNA NPs. Our work showed the small operation volume (i.e., high

reaction concentration) resulted in larger particle size due to the low-degree ionization of the

polymers and the consequent less compact interaction.

Though the conventional perception was that the small NPs are superior to the large ones

in systemic delivery because the large ones are prone to be cleared away from the blood

stream [34], it is still difficult to reach a conclusion in gene transfection. Size is also a key

factor controlling the intracellular fate [35]. For example, the small NPs could have higher

cellular uptake efficiency than the large NPs, but the latter could exhibit higher endosome

escape capacity and thus yield enhanced gene transfection [36]. However, the mechanisms

for enhanced transfection of the large NPs have not been fully elucidated yet. Multiple factors

could be involved in the gene transfection, such as physical and biological issues. For

example, it was reported that gravitational sedimentation of NPs was an important factor that

benefited the large NPs for the in vitro transfection [2].

PEI and DNA are polyelectrolyte, and their interaction can be treated as polyelectrolyte

complex. The chain conformations in linear polymers with a uniformly distributed charge

reflect a balance among the intramolecular repulsion of charged segments [37]. Therefore, the

high ionization results in a flexible linear conformation, while the polymers at low ionization

tend to form a curl conformation [38, 39], because of insufficient intramolecular repulsion.

Low concentration facilitates the ionization of the charged polymers [40], and the highly

ionic and extended polymer chains can readily bind with another polymers with the

counterion with strong interaction. Conversely, the polymers with low ionization and curled

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confirmation tend to form less compact polyelectrolyte complex with the counterion

polymers.

The interaction of ionic components can be described using the Coulomb's law:

F=k q1 q2

r2

where k is Coulomb's constant (k ≈ 9×109 N m2 C−2), q1 and q2 are the signed magnitudes of

the charges, and the scalar r is the distance between the charges. Generally, the increased

charges and the reduced distance between the ionic components result in the strong

interaction force, forming the compact complex. This can be accounted for the formation of

small and compact NP in the low concentration group (PEI/DNA low) but large NP in the high

concentration group.

An interesting finding from our studies was that the cellular uptake percentages

(represented by the positive rate) of both NPs were close, but the uptake amount (represented

by the total fluorescence intensity) was significantly higher in the PEI/DNAhigh NPs than the

PEI/DNAlow NPs. It suggested that the macropinocytosis pathway was more highly efficient

to engulf the NPs compared to the clathrin-mediated uptake. Macropinocytosis is associated

with the generation of the large endocytic vesicles by driving by the actins and plasma

membrane evaginates, thus enabling to engulf a large number of extracellular substances.

Our results indicated that macropinocytosis facilitated a greater amount of NPs into a cell

than other endocytosis pathways. Moreover, the large PEI/DNAhigh NPs had higher

cytoplasmic dissociation efficiency, and led to enhanced intranuclear delivery.

PEI-based vectors have poor systemic delivery efficiency in the blood circulation, which

results in low overall delivery efficiency in vivo and hinders the systemic therapy in clinical

application [41]. Recently, gene therapy via local-regional administration has obtained great

success, representing the first directly administered gene therapy product (Luxturna)

approved in the U.S. for hereditary retinal dystrophies via subretinal injection. Therefore, the

local-regional administration provides a promising strategy for bypassing the inherent

shortcomings of PEI.

4 Conclusions

It was first revealed that the formation of PEI/DNA NPs was significantly affected by the

reaction concentration. The PEI and DNA that complexed at a high concentration tended to

form a large and less compact NPs, compared to that at a low concentration. As a result, the

large PEI/DNAhigh NPs performed the enhanced gene transfection via the mechanisms of

13

macropinocytosis-mediated cellular uptake, effective dissociation and DNA release, and the

enhanced intranuclear delivery. By contrast, the PEI and DNA that complexed at a low

concentration tended to form a small and compact NPs, which preferred the clathrin-mediated

endocytosis pathway and confronted the endosome barrier against effective cytoplasmic

delivery. These findings shed light on the importance of formulation process optimization

(e.g., reaction concentration) that has long since been ignored, and thus provide better

understanding of the formulation process effect on nano-structural properties and gene

transfection, laying a theoretic basis for rational design of experimental process.

5 Materials and Methods

5.1 Materials

Linear PEI25K was purchased from Polysciences (USA). Chlorpromazine, nystatin, and

cytochalasin D were purchased from Sigma-Aldrich (USA). Nuc-Cyto-Mem Preparation Kit

were purchased from Applygen Technologies (Beijing, China). The plasmid of peGFP-N1

encoding enhanced green fluorescent protein, pRFP encoding red fluorescent protein, and

pGL4.13 encoding luciferase were propagated in a DH5-strain of E. coli and purified by

using a QIAGEN Plasmid Maxi Kit (Germany). YOYO-1, LysoTracker Red DND-99, DIO,

dextran rhodamine B (MW 70 kDa) were purchased from Invitrogen (USA). The 5-TAMRA-

SE was purchased from MedChem Express (USA). Fetal bovine serum (FBS) and RPMI

1640 medium were purchased from Thermo Fisher Scientific (USA). Hoechst 33342 Staining

Solution for Live Cells, DAPI staining solution, RIPA lysis buffer, 0.25% trypsin-EDTA,

BCA microplate protein assay kit, and ROS detection kit were obtained from Beyotime

Institute of Biotechnology (Haimen, China). Luciferase Assay System Kit was purchased

from Promega (USA). Anti-DR5, anti-TRAIL, and anti-GAPDH were purchased from Cell

Signaling Technology (USA). All of the other reagents were of analytical grade, and

purchased from Sinopharm Chemical Reagent Co., Ltd (Shanghai, China). Branch PEI25K was

purchased from Sigma-Aldrich (USA).

5.2 Cell culture and animals

Human cervical cancer HeLa cells, MCF-7 cells, H/T cells, and A549T cells were

obtained from the Cell Bank of Chinese Academy of Sciences (Shanghai, China). DC2.4

cells, a murine dendritic cell line [42], were kindly provided by Prof. Ying Hu (Wenzhou

Medical University, Zhejiang, China).The cells were cultured in Gibco® RPMI 1640 medium

14

containing 10% FBS, 100 μg/mL streptomycin, and 100 U/mL penicillin in a humidified

atmosphere at 37°C and 5% CO2. The female BALB/c nude mice (3–4 weeks old) were

purchased from SLAC Animal Inc. (Shanghai, China) and housed in specific pathogen-free

conditions. The in vivo experimental procedures were approved by the Animal Care and Use

Committee of Shanghai Institute of Materia Medica.

5.3 Preparation of two types of the PEI/DNA NPs

Two types of the PEI/DNA NPs were prepared using the same procedure and the same

amount of PEI and DNA in pure water, but at different concentrations. The high-

concentration group (PEI/DNAhigh) was prepared using 0.2 mg/mL of plasmid DNA and PEI

(equal to a total 20 μL), while the low-concentration group (PEI/DNA low) using 0.02 mg/mL

of DNA and PEI (equal to a total 200 μL). In specific, the PEI aqueous solution was added to

the equal volume of DNA aqueous solution (1.3:1, w/w), and after gentle mixing, the mixture

was incubated at 37°C for 30 min. The NPs were freshly prepared before use.

5.4 Particle size and zeta potential analysis

The particle size and zeta potential of the PEI/DNA NPs were measured in water or

serum-containing medium using the ZetaSizer Nano ZS90 Size Analyzer (Malvern

Panalytical, Brighton, UK), and the stability of the NPs was evaluated by detecting the

particle size change at varying time points. The final concentration was diluted to equally 3

μg/mL DNA with the final volume 1 mL for particle size and zeta potential analysis of each

formulation.

5.5 Transfection experiments

HeLa cells were seeded in the 12-well plates at a density of 1 × 105 cells per well. After

20-h culture, the cells were treated with the same amount (1 μg DNA per well) of the

PEI/DNA NPs dispersed in the fresh RPMI 1640 medium without FBS for 4 h at 37 °C, and

then cultured with the fresh completed medium for 24 h to allow gene expression. The

plasmid DNA reporter (peGFP-N1, pRFP, or pGL4.13) was used in the transfection studies.

The transfection efficiency of peGFP-N1 or pRFP was measured using a flow cytometer (BD

Pharmingen, San Jose, CA, USA), and data analysis was performed using FlowJo software.

For the transfection efficiency assay of pGL4.13, the cells were harvested and treated using

200 μL of the RIPA lysis buffer. After centrifugation at 12,000 g for 20 min, the luciferase

activity of the supernatants was detected using the Luciferase Assay Kit, and luminescence

15

was measured with the EnSpire Multimode Plate Reader (PerkinElmer, Waltham, MA,

USA). Luminescence was normalized to the protein concentration of each sample, which was

measured using the BCA Microplate Protein Assay Kit. Luciferase activity was designated as

RLU/mg protein. Moreover, DC2.4 cells, BMDCs, MCF-7 cells, H/T cells and A549T cells

were also performed the transfection experiment as the HeLa cells.

5.6 Cellular uptake of the two groups of PEI/DNA NPs

The plasmid DNA was labeled with YOYO-1 dye. The HeLa cells were seeded into the

12-well plates at a density of 1 × 105 cells per well. After 20-h culture, they were treated with

the same amount of the PEI/DNA NPs in 1 mL fresh RPMI 1640 medium without FBS for 4

h at 37 °C. The cells were thoroughly washed with PBS and fixed in 4% paraformaldehyde.

After staining with DAPI, the cells were observed by CLSM (TCS-SP8 STED; Leica

Microsystems, Mannheim, Germany). For quantitative measurement, the cells were

thoroughly washed and collected, and then analyzed with a flow cytometer using the FL1

channel. Moreover, the cellular uptake experiments were also performed in DC2.4 cells and

BMDCs.

5.7 Observation of cellular uptake

The PEI/DNA NPs were labeled with 5-TAMRA-SE dye. The HeLa cells were seeded

into the glass plates. After 20-h culture, the cell membrane was labeled with DIO dye and

then treated with the same amount of the PEI/DNA NPs in 1 mL fresh RPMI 1640 medium

without FBS. The living cells were immediately observed by TIRFM (Olympus, Japan). The

fluorescence images were captured every 5 s, and the nanoparticles were analyzed by single-

particle tracking (SPT) technique programmed by MATLAB software.

5.8 Influence of polyelectrolyte concentrations on the structure of PEI chains via zeta

potential and hydrodynamic diameter analysis

Zeta potential and hydrodynamic diameter of the NPs were measured to investigate the

structure of PEI chains at various polyelectrolyte concentrations. In brief, the PEI aqueous

solution was prepared at different concentrations (0.02, 0.026, 0.05, 0.1, 0.2, 0.26, 0.5, and

1.0 mg/mL). The zeta potential and hydrodynamic diameter of the PEI molecules were

measured using the ZetaSizer Nano ZS90 Size Analyzer (Malvern Panalytical Ltd, UK). In

addition, the zeta potential and hydrodynamic diameter of the PEI/DNAlow NPs (CPEI = 0.026

mg/mL) and the PEI/DNAhigh NPs (CPEI = 0.26 mg/mL), were also measured.

16

5.9 Analysis of the effects of gene transfection by endocytosis inhibitors

The plasmid peGFP-N1 was used as a reporter gene. The HeLa cells were seeded in the

12-well plates at a density of 1 × 105 cells per well. After 20-h culture, the cells were treated

with various endocytosis inhibitors for 1 h (chlorpromazine at 10 μM, 20 μM, or 40 μM;

nystatin at 10 μM, 20 μM, or 40 μM and cytochalasin D at 1 μM, 5 μM, or 10 μM). The cells

were then treated with the same amount of PEI/DNA low or PEI/DNAhigh NPs in the fresh

RPMI 1640 medium without FBS for 4 h at 37 °C. After 4-h treatment of the NPs, the cells

were cultured with the fresh complete RPMI 1640 medium for 24 h to allow gene expression.

The fluorescence images were observed by fluorescence microscope (Zeiss, Germany).

Meanwhile, the cells were harvested and analyzed with a flow cytometer.

5.10 Observation of intracellular distribution of the NPs

The plasmid DNA was labeled with the YOYO-1 dye. The HeLa cells were seeded into

the glass plates. After 20-h culture, the cell nuclei were stained with hoechst 33342. The cells

were then treated with the NPs for 4 h at 37 °C, and at the mark of 2 h during the cellular

uptake experiment, a macropinosome dye (dextran rhodamine B, 70 kDa) was added to the

culture medium with another 2-h incubation with the cells. The cells were stained with

LysoTracker Red DND-99 for 30 min. The cells were thoroughly washed with PBS, fixed in

4% paraformaldehyde, and observed by CLSM. The co-localization percentage was analyzed

by ImageJ software.

5.11 Atomic force microscopy (AFM) observation

The PEI/DNA NPs were added to the surface of freshly cleaved mica for 20 min. The

mica surface was then gently rinsed with sterile water for 10 times, followed by AFM

observation (Bruker Scientific Instruments, Bremen, Germany) in the peakforce mode using

ScanAsyst-Fluid+ probes with standard silicon tips (Bruker). The PEI solution was used as the

control group. AFM images were analyzed using NanoScope Analysis software. The average

value of particle peak height was a result of counting 589 particles in the PEI/DNAhigh group

and 2379 particles in the PEI/DNAlow group.

5.12 Stimulated emission depletion (STED) microscopy

The plasmid DNA was labeled with YOYO-1 dye, and PEI was labeled with 5-TAMRA-

SE dye. The PEI/DNA NPs were added to the surface of freshly cleaved mica and incubated

17

for 20 min. The mica surface was gently rinsed with distilled water for 10 times and dried at

room temperature. The samples were observed by CLSM operating in the STED mode.

5.13 Fluorescence resonance energy transfer (FRET) effect

PEI was chemically labeled with Cy5 NHS ester, and the plasmid DNA was chemically

labeled with Cy3 dye. PEICy5 and DNACy3 were mixed at the same volume but at different

mass ratios (0.2:1, 0.5:1, 1.3:1, 2:1). The mixtures were incubated at 37 °C for 30 min. The

observation of FRET effect was performed by measuring the emission fluorescence intensity

of Cy3 at 547 nm using a fluorospectrometer (F4600; Hitachi, Japan). The HeLa cells were

seeded into the glass slices at a density of 1 × 105 cells per well. After 20-h culture, the cell

nuclei were stained with Hoechst 33342 Staining Solution for Live Cells for 10 min. The

cells were then treated with the same amount of the PEICy5/DNACy3 NPs in the fresh RPMI

1640 medium without FBS for 4 h at 37 °C. To investigate the disassociation of PEI and

DNA, the cells were thoroughly washed with PBS and fixed in 4% paraformaldehyde at the

time points of 4, 8, and 12 h, followed by CLSM observation. For quantitative analysis of the

FRET efficiency, the cells were analyzed by flow cytometry. The PEI/DNA and PEI/DNACy3

NPs were set as the unlabeled and donor-labeled controls.

The FRET efficiency of the two groups of NPs in the cell was quantitatively analyzed by

flow cytometry [43]. The FRET efficiency (E) was calculated according to the following

equation:

E=1−I DA−I 0

ID−I 0,

where I0 was the fluorescence intensity of unlabeled sample, ID was the fluorescence

intensity of the donor-labeled sample, and IDA that of the double-labeled sample.

5.14 Nuclear transport of the two groups of PEI/DNA NPs

The plasmid DNA was chemically labeled with Cy3 dye. The HeLa cells were seeded into

the 12-well plates at a density of 1 × 105 cells per well. After 20-h culture, they were treated

with the same amount of PEI/DNA NPs in the fresh RPMI 1640 medium without FBS for 4 h

at 37 °C, and then cultured with the fresh complete RPMI 1640 medium. The cells were

thoroughly washed with PBS and harvested at 4, 8, and 12 h time points. The cell nuclei were

isolated using the Nuc-Cyto-Mem Preparation Kit and analyzed using flow cytometry.

18

5.15 In vitro transfection and cytotoxicity assay of PEI/pTRAIL NPs

As a therapeutic gene, pTRAIL was used to investigate the in vitro treatment efficacy. The

HeLa cells were seeded in the 12-well plates at a density of 1 × 105 cells per well. After 20-h

culture, the cells were treated with the same amount (1 μg pTRAIL per well) of the

PEI/pTRAIL NPs dispersed in the fresh RPMI 1640 medium for 4 h at 37 °C, and then

cultured with the fresh completed medium for 48 h to allow gene expression. After

transfection, the cells were harvested for Western blotting analysis to detect the TRAIL

expression.

For the in vitro cytotoxicity assay, the HeLa cells were seeded in the 96-well plates. For

the control groups, the PEI/pDNA NPs were prepared by using empty plasmid. The cells

were treated with the NPs dispersed in the fresh RPMI 1640 medium without FBS for 4 h at

37 °C, and then cultured with the fresh completed medium for 48 h. Cytotoxicity were then

measured by a standard MTT assay. Briefly, MTT solution (20 μL, 5 mg/mL) was added to

each well, after which the cells were incubated for another 4 h. After removal of the medium,

200 μL of DMSO was added to each well, and the absorbance was measured at 490 nm using

a microplate reader (Thermo Fisher Scientific, Waltham, MA, USA). The cell viability (%)

was calculated according to the following equation:

Cell viability （%）=(OD test−ODDMSO)

(ODcontrol−ODDMSO)×100

5.16 Measurement of intracellular ROS

After 24-h transfection of HeLa cells with the PEI/pTRAIL NPs as the procedure described

above, the cells were harvested and stained using a ROS detection kit according to the

manufacture’s protocol. The samples were analyzed by flow cytometry.

5.17 In vivo antitumor experiments with local administration

The subcutaneous tumor xenograft model was developed by s.c. injection of the HeLa

cells (4 × 106 cells/mouse). When the tumor volume reached about 100 nm3, the mice were

daily treated with PBS, PEI/pTRAILlow, and PEI/pTRAILhigh NPs via intratumoral

administration at a dose of 50 µg/kg of pTRAIL per mouse (eight mice per group), around the

1/10 dose of the commonly used dose of i.v. injection [23, 25]. After injection, the pinhole

was sealed by medical glue to accelerate the healing. The body weight and tumor size

(measured with a caliper) were recorded. The estimated tumor volume was calculated as

follows:

19

V=(a2× b)/2,

where a is the shortest diameter and b is the longest diameter.

At the experimental endpoint, the mice were sacrificed and the major organs and tumors

were harvested to measure the organ coefficient and tumor weight. The organ coefficient was

calculated by comparing each organ weight between a treatment group and the PBS control

group, and the tumor inhibition rate was calculated by comparing the tumor weight between a

treatment group and the PBS control group. The organs were fixed in 4% paraformaldehyde

for histological examination by hematoxylin and eosin staining. Immunohistochemical

staining of the tumor slices was performed to observe TRAIL expression, and Western blot

analysis was conducted to detect the TRAIL and DR5 expression. The TUNEL assay was

performed to detect apoptosis.

5.18 In vivo gene therapy experiments with regional administration

Abdominally disseminated cervical tumor model was established by i.p. inoculation of the

HeLa cells (4 × 106 cells/mouse) into the nude mice. Six days after inoculation, the mice were

treated with water, PEI/pTRAILlow, and PEI/pTRAILhigh NPs via i.p. injection at a daily dose

of 0.25 mg/kg of pTRAIL per mouse (six mice per group). After eleven times treatment, the

mice received no further additional treatment for another six days. The body weight was

detected every day. At the experimental endpoint, the mice were sacrificed and the major

organs and tumors in the peritoneal cavity were carefully harvested to measure the organ

coefficient and tumor weight.

5.19 Statistical analysis

All quantitative data are presented as the mean ± standard deviation (SD), all of which

were repeated at least three times. Statistical significance was analyzed with the Student’s t-

test. P values less than 0.05 were considered statistically significant.

Acknowledgments

We are thankful for the support from 973 Program, China (2014CB931900) and NFSC,

China (81402883, 81422048, 81673382, and 81521005), the Strategic Priority Research

Program of CAS (XDA12050307), Scientific Research and Equipment Development Project

(YZ201437), SANOFI-SIBS Scholarship Program, Youth Innovation Promotion Association

of CAS and the Fudan-SIMM Joint Research Fund (FU-SIMM20174009). We also thank the

20

technical assistance from the Molecular Imaging and Electron Microscopy Core Facilities,

SIMM.

Supporting information

Figure S1–S9 and Supplementary Video.

Reference:1. Ogris M, Steinlein P, Kursa M, Mechtler K, Kircheis R, Wagner E. The size of DNA/transferrin-PEI complexes is an important factor for gene expression in cultured cells. Gene Ther. 1998; 5: 1425-33.2. Pezzoli D, Giupponi E, Mantovani D, Candiani G. Size matters for in vitro gene delivery: investigating the relationships among complexation protocol, transfection medium, size and sedimentation. Sci Rep. 2017; 7: 44134.3. Pezzoli D, Olimpieri F, Malloggi C, Bertini S, Volonterio A, Candiani G. Chitosan-Graft-Branched Polyethylenimine Copolymers: Influence of Degree of Grafting on Transfection Behavior. PloS One. 2012; 7: e34711.4. Malloggi C, Pezzoli D, Magagnin L, De Nardo L, Mantovani D, Tallarita E, et al. Comparative evaluation and optimization of off-the-shelf cationic polymers for gene delivery purposes. Polym Chem. 2015; 6: 6325-39.5. Lucotti A, Tommasini M, Pezzoli D, Candiani G. Molecular interactions of DNA with transfectants: a study based on infrared spectroscopy and quantum chemistry as aids to fluorescence spectroscopy and dynamic light scattering analyses. RSC Adv. 2014; 4: 49620-7.6. Pack DW, Hoffman AS, Pun S, Stayton PS. Design and development of polymers for gene delivery. Nat Rev Drug Discov. 2005; 4: 581-93.7. Godbey WT, Wu KK, Mikos AG. Poly(ethylenimine) and its role in gene delivery. J Control Release. 1999; 60: 149-60.8. Kunath K, von Harpe A, Fischer D, Peterson H, Bickel U, Voigt K, et al. Low-molecular-weight polyethylenimine as a non-viral vector for DNA delivery: comparison of physicochemical properties, transfection efficiency and in vivo distribution with high-molecular-weight polyethylenimine. J Control Release. 2003; 89: 113-25.9. Rungsardthong U, Ehtezazi T, Bailey L, Armes SP, Garnett MC, Stolnik S. Effect of polymer ionization on the interaction with DNA in nonviral gene delivery systems. Biomacromolecules. 2003; 4: 683-90.10. Jaqaman K, Loerke D, Mettlen M, Kuwata H, Grinstein S, Schmid SL, et al. Robust single-particle tracking in live-cell time-lapse sequences. Nat Methods. 2008; 5: 695-702.11. Clemens DL, Lee BY, Horwitz MA. Francisella tularensis enters macrophages via a novel process involving pseudopod loops. Infect Immun. 2005; 73: 5892-902.12. Rejman J, Bragonzi A, Conese M. Role of clathrin- and caveolae-mediated endocytosis in gene transfer mediated by lipo- and polyplexes. Mol Ther. 2005; 12: 468-74.13. Iwabuchi K, Handa K, Hakomori S. Separation of "glycosphingolipid signaling domain" from caveolin-containing membrane fraction in mouse melanoma B16 cells and its role in cell adhesion coupled with signaling. J Biol Chem. 1998; 273: 33766-73.14. Kruth HS, Jones NL, Huang W, Zhao B, Ishii I, Chang J, et al. Macropinocytosis is the endocytic pathway that mediates macrophage foam cell formation with native low density lipoprotein. J Biol Chem. 2005; 280: 2352-60.15. Rejman J, Oberle V, Zuhorn IS, Hoekstra D. Size-dependent internalization of particles via the pathways of clathrin- and caveolae-mediated endocytosis. Biochem J. 2004; 377: 159-69.16. McMahon HT, Boucrot E. Molecular mechanism and physiological functions of clathrin-mediated endocytosis. Nat Rev Mol Cell Biol. 2011; 12: 517-33.17. El-Sayed A, Harashima H. Endocytosis of gene delivery vectors: from clathrin-dependent to lipid raft-mediated endocytosis. Mol Ther. 2013; 21: 1118-30.

21

18. Hamasaki M, Araki N, Hatae T. Association of early endosomal autoantigen 1 with macropinocytosis in EGF-stimulated A431 cells. Anat Rec A Discov Mol Cell Evol Biol. 2004; 277: 298-306.19. Love KT, Mahon KP, Levins CG, Whitehead KA, Querbes W, Dorkin JR, et al. Lipid-like materials for low-dose, in vivo gene silencing. Proc Natl Acad Sci USA. 2010; 107: 1864-9.20. Amyere M, Mettlen M, Van DS, Platek A. Origin, originality, functions, subversions and molecular singalling of macropinocytosis. Int J Med Microbiol. 2002; 291: 487-94.21. Khalil IA, Kogure K, Akita H, Harashima H. Uptake pathways and subsequent intracellular trafficking in nonviral gene delivery. Pharmacol Rev. 2006; 58: 32-45.22. Mintzer MA, Simanek EE. Nonviral Vectors for Gene Delivery. Chem Rev. 2009; 109: 259-302.23. Pan Z, Kang X, Zeng Y, Zhang W, Peng H, Wang J, et al. A mannosylated PEI-CPP hybrid for TRAIL gene targeting delivery for colorectal cancer therapy. Polym Chem. 2017; 8: 5275-85.24. Tan J, Wang HY, Xu F, Chen YZ, Zhang M, Peng HG, et al. Poly-gamma-glutamic acid-based GGT-targeting and surface camouflage strategy for improving cervical cancer gene therapy. J Mater Chem B. 2017; 5: 1315-27.25. Xu F, Zhong H, Chang Y, Li D, Jin H, Zhang M, et al. Targeting death receptors for drug-resistant cancer therapy: Codelivery of pTRAIL and monensin using dual-targeting and stimuli-responsive self-assembling nanocomposites. Biomaterials. 2018; 158: 56-73.26. Wang SL, El-Deiry WS. TRAIL and apoptosis induction by TNF-family death receptors. Oncogene. 2003; 22: 8628-33.27. Jang JY, Kim SJ, Cho EK, Jeong SW, Park EJ, Lee WC, et al. TRAIL enhances apoptosis of human hepatocellular carcinoma cells sensitized by hepatitis C virus infection: therapeutic implications. PLoS One. 2014; 9: e98171.28. Park EJ, Min KJ, Choi KS, Kubatka P, Kruzliak P, Kim DE, et al. Chloroquine enhances TRAIL-mediated apoptosis through up-regulation of DR5 by stabilization of mRNA and protein in cancer cells. Sci Rep. 2016; 6: 22921.29. Budker VG, Monahan SD, Subbotin VM. Loco-regional cancer drug therapy: present approaches and rapidly reversible hydrophobization (RRH) of therapeutic agents as the future direction. Drug Discov Today. 2014; 19: 1855-70.30. Chen J, Guo Z, Tian H, Chen X. Production and clinical development of nanoparticles for gene delivery. Mol Ther Methods Clin Dev. 2016; 3: 16023.31. Qiu N, Liu X, Zhong Y, Zhou Z, Piao Y, Miao L, et al. Esterase-Activated Charge-Reversal Polymer for Fibroblast-Exempt Cancer Gene Therapy. Adv Mater. 2016; 28: 10613-22.32. Odendahl K, Solass W, Demtroder C, Giger-Pabst U, Zieren J, Tempfer C, et al. Quality of life of patients with end-stage peritoneal metastasis treated with Pressurized IntraPeritoneal Aerosol Chemotherapy (PIPAC). Eur J Surg Oncol. 2015; 41: 1379-85.33. Yin H, Kanasty RL, Eltoukhy AA, Vegas AJ, Dorkin JR, Anderson DG. Non-viral vectors for gene-based therapy. Nat Rev Genet. 2014; 15: 541-55.34. Zhou Z, Liu X, Zhu D, Wang Y, Zhang Z, Zhou X, et al. Nonviral cancer gene therapy: Delivery cascade and vector nanoproperty integration. Adv Drug Deliv Rev. 2017; 115: 115-54.35. Behzadi S, Serpooshan V, Tao W, Hamaly MA, Alkawareek MY, Dreaden EC, et al. Cellular uptake of nanoparticles: journey inside the cell. Chem Soc Rev. 2017; 46: 4218-44.36. Zhu D, Yan H, Zhou Z, Tang J, Liu X, Hartmann R, et al. Detailed investigation on how the protein corona modulates the physicochemical properties and gene delivery of polyethylenimine (PEI) polyplexes. Biomater Sci. 2018; 6: 1800-17.37. Chremos A, Douglas JF. Influence of higher valent ions on flexible polyelectrolyte stiffness and counter-ion distribution. J Chem Phys. 2016; 144: 164904.38. Dobrynin AV, Rubinstein M. Theory of polyelectrolytes in solutions and at surfaces. Prog Polym Sci. 2005; 30: 1049-118.39. Stevens MJ, Kremer K. Form-Factor of Salt-Free Linear Polyelectrolytes. Macromolecules. 1993; 26: 4717-9.40. Tsuchida E. Formation of Polyelectrolyte Complexes and Their Structures. JMS-Pure Appl Chem. 1994; A31: 1-15.

22

41. Zhou ZX, Liu XR, Zhu DC, Wang Y, Zhang Z, Zhou XF, et al. Nonviral cancer gene therapy: Delivery cascade and vector nanoproperty integration. Adv Drug Deliver Rev. 2017; 115: 115-54.42. Shen ZH, Reznikoff G, Dranoff G, Rock KL. Cloned dendritic cells can present exogenous antigens on both MHC class I and class II molecules. J Immunol. 1997; 158: 2723-30.43. Nagy P, Vereb G, Damjanovich S, Matyus L, Szollosi J. Measuring FRET in flow cytometry and microscopy. Curr Protoc Cytom. 2006; Chapter 12: Unit12 8.

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Figures

Scheme 1. The scheme of self-assembly process of the two groups of PEI/DNA NPs.

24

Figure 1. The cellular uptake results of the two groups of NPs. (A) Confocal images.

NPs are shown in green. Scale bar, 20 μm. (B-D) FACS analysis of cellular uptake, and the

quantitative analysis of the cellular uptake rate and total fluorescence intensity.

25

Figure 2. The results of transfection experiments of the two groups of PEI/DNA NPs. (A, F) Fluorescence images of GFP and RFP expression. GFP is shown in green, and RFP

is shown in red. Scale bar, 100 μm. (B-D, G-H) FACS analysis of GFP and RFP expression

in HeLa cells, and the quantitative analysis of positive transfection rate and total

fluorescence intensity of HeLa cells. (E) Luciferase expression.

26

Figure 3. AFM measurements results. (A) The 2D and 3D AFM images of the NPs. Scale

bar, 1 μm. (B) Section analysis of the NPs in the 2D AFM images. (C) Particle peak height of

the two groups of NPs.

27

Figure 4. The STED images of the PEI/DNAlow NPs (A) and the PEI/DNAhigh NPs (B). PEI

is shown in red, DNA is shown in green.

28

Figure 5. TIRFM analysis. (A)The cellular uptake of the PEI/DNAhigh NPs was divided into

three parts. (B) The trajectory analysis of the PEI/DNAhigh NPs, and the amplified trajectory of

the bulky NPs. (C) The cellular uptake of the bulky NPs tabbed with the trajectory timely; (D) the normalized lifetime histogram of trajectories; (E) mean square displacement (MSD)

analysis of the bulky NP trajectories in and out of the cell in Figure 5D; (F) the trajectory of

the bulky NPs is shown as x coordinate, y coordinate and amplitude over time. Scale bar, 20

μm.

29

Figure 6. Effects of gene transfection by endocytosis inhibitors. (A, C, E) The

transfection relative positive level. (B, D, F) The protein expression relative positive level.

30

Figure 7. The results of co-localization of the lysosomes and NPs. (A) The 2D and 3D

confocal images. DNA is shown in green, lysosomes stained with LysoTracker Red DND-99

are shown in red, and the cell nuclei are showed in blue. (B) The co-localization percentage

of the lysosomes and NPs. Scale bar, 20 μm.

31

Figure 8. The results of co-localization of the macropinosomes and NPs. (A) The 2D

and 3D confocal images. DNA is shown in green, macropinosomes labeled with Dextran

Rhodamine B are shown in red, and the cell nuclei are showed in blue. (B) The co-

localization percentage of the macropinosomes and NPs. Scale bar, 20 μm.

32

Figure 9. Observation of the disassociation of DNA and PEI by FRET. (A) The FRET

effect was present in the PEICy5/DNACy3 in varying mass ratios. (B) The 3D confocal images

of the disassociation of the two groups of NPs in the cell at 4, 8, and 12 h. PEI was shown in

red, DNA was shown in green, the cell nuclei were shown in blue, and the co-localization of

PEI and DNA was shown in yellow. Scale bar, 20 μm. (C) Quantitative analysis of the FRET

efficiency.

33

Figure 10. Nuclear uptake of the two groups of NPs. (A) Quantitative analysis of the

nuclear uptake rate. (B) The total fluorescence intensity of the nuclei.

34

Figure 11. (A) Western blot analysis results of TRAIL expression level in HeLa cells after

gene transfection of the two groups of PEI/pTRAIL NPs. (B) The results of anti-tumor activity

of the two groups of PEI/pTRAIL NPs in vitro.

35

Figure 12. (A) Tumor volume changes in the treatment regimen (n=8). (B) The presentation

of tumor tissues after treatment. (C, D) The tumor weight at the end point and the tumor

inhibition rate. (E) The survival rate in the treatment regimen. (F) Western blot analysis

results of TRAIL expression and DR5 level in tumor tissues. (G) Images of

immunohistochemical staining for the examination of TRAIL protein expression. (H) Images

of TUNEL-stained tumor sections for evaluating apoptosis. Scale bar, 20 μm.

36

Figure 13. Therapeutic efficacy of HeLa i.p. tumors treated with the two groups of PEI/pTRAIL NPs. (A) Treatment regime. (B) The average tumor weights. (C) The tumor

inhibition rate. (D) Dissected tumor nodules of mice (n=6). (E) The body weight changes

over the regimen. (F) The organ coefficients.

37

1